Combustion system



Feb. 16, 1965 P. M. HOLL cousus'non svsmm Filed June 19, 1963 invade/-United States Patent 3,169,369 CGMBUSTION SYSTEM Peter M. Hell, WalnutCreek, Caiih, assignor to General Electric Company, a corporation of NewYork Filed June 19, 1963, Ser. No. 289,045 12 Claims. ((31. oil-39.66)

The present invention relates to a combustion system and, moreparticularly, to a reverse flow combustion systern adapted for use atthe downstream or aft end of a gas turbine engine.

Small gas turbine powerplants are are compact and that use a singlereverse flow combustor at the downstream end of the powerplant are knownand a typical powerplant is shown in US. Patent 2,553,867. Such enginesuse a single combustion chamber at the aft end of the powerplantgenerally symmetrical about the longitudinal centerline of the engine.Because of the location at the aft end of the powerplant the singlecombustor is of the reverse flow type, and the combustor inlet from theupstream compressor and the combustor exit from the combustion zone tothe turbine are concentric annular passages. Such engines are generallydesigned to be low cost, lightweight compact engines. In order toaccomplish these objectives it is desirable to use low cost and easilyformed materials as much as possible. In the combustion end of theengine it is necessary to have a predictable and uniform turbine inlettemperature distribution and highly advantageous to have a turbine inlettemperature profile which ensures that the turbine bucket roots are cooland the warmer temperatures occur at the tip of the turbine buckets.This temperature profile must be obtained of course at high combustionefiiciency, with low pressure loss and easy ignition in the combustionzone. It is then possible to take advantage of such a desirabletemperature profile in the turbine design. By keeping the roots of theturbine buckets relatively cool it is possible to withstand higher rootstresses and thus minimize bucket mass and associated disk loads. Thisallows increased bucket life for a given inlet temperature, or a higherinlet temperature for a given life. Additionally, the turbine inlettemperature must be uniform about the complete circumference of theturbine inlet. Thus, such design objective require specific combustionsystems for a given engine.

The main object of the present invention is to provide a reverse flowcombustion system that is low cost, lightweight and efiicient, and thatmaintains a temperature profile at the turbine inlet for better coolingof the roots of the turbine buckets.

Another object is to provide such a combustion system which, by means ofdome cap geometry and particularly oriented dome louvers takes advantageof the natural flow of air into the combustor to achieve bettercombustion performance including stabilizing the flame where desired.

A further object is to provide such a system which uses a centerbodymember to direct exhaust to the turbine, to promote direct cooling ofthe turbine buckets, and provide better mixing of the hot combustiongases and the cooling air in the novel combustor.

Briefly stated, the invention provides a reverse flow combustion systemincluding the combustor to be used on the aft end of a gas turbineengine next to the turbine which provides an annular air inletcircumterentially around the turbine and then funnels the air between apair of conical-cylindrical members in an annular passage and directs asubstantial percentage of the air into a combustion zone throughparticularly oriented louvers whereupon it is reversed and flows forwardand out an annular passage concentric with the inlet annular passage andto a point of exhaust. A centerbody is disposed in the combustor chamberand is conical in shape, and the centerice body is provided with a domecap at its cone end for directing airflow to achieve cooling of theturbine roots. An ignition means is provided at a specific locationwhere there is a locally rich mixture of the fuel and air.,

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed the invention will be better understood fromthe following de-' scription taken in connection with the accompanyingdrawing in which: 7

FIG.. 1 is a diagrammatic cross-sectional view of the combustion system;I

FIG. 2 is an end view of the dome closure; and

FIG. 3 is a graphic illustration of the temperature profile obtainableby the instant invention.

Referring first to FIG. 1, there is shown the reverse flow combustionsystem of the instant invention which system includes a combustor andmay be hung on the downstream end of a small gas turbine powerplant ofthe type shown in the above-mentioned patent. Only so much of thecombustion system as is necessary for its understanding is shown and itwill be understood that it may be applicable to a number of powerplantarrangements of the type shown in the above-mentioned patent. -Air froman upstream compressor source'is funneled into the combustion system,and to the combustor generally indicated at 9 between a pair ofconcentric shells l0 and 11 to define an annular air passage 12 aroundthe outer periphery of a turbine 13 which, in a powerplant of the typefor which the instant combustion system is adapted, will generally bemounted as shown. In order to get the air into the combustion zone, anouter combination conical-cylindrical casing 14, which is closed at itscone end 15, is secured to outer shell It at flange 16 and an innerconcentric combination conical-cylindrical liner 17 is secured to theinner.

shell 11 by any suitable means such as a sliding fit 18. The inner lineris perforated at 19 for a selected length by suitable openings such asslots, holes, etc. which are well known. Preferably, plain holes asshown are used. For purposes that will be apparent as the descriptionproceeds,

liner 17 is closed at its cylindrical end by a double conical domeclosure generally indicatedat 20. It will be noted that casing 14 andliner 17 are spaced aft in a symmetrical and axially aligned manner toform a coned and then cylindrical zone in a manner to provide acontinuation 21 of annular air passage 12, and that such continuationdecreases in cross-sectional area in the downcylinder shape provides aplenum chamber eiiect-for maximum pressure drop across the liner walltointroduce the required mass of air with the required penetration intothe primary combustion zone within the cylindrical part.

In order to obtain good mixing and fuel distribution in the cornbustor,the double conical dome closure is important. It includes an inner cone22 and an outer cone 23. The outer cone is a continuation of the innercone and opens out fiatter and away from the inner cone. Thisarrangement provides completely separate zones of air introduction whosedesirability will be apparent. For providing initial air to mix with andfurther atomize the incoming fuel, the inner cone 22 is provided with aseries of substantially radial louvers 24 extending around the Ijuncture that good ignition will occur.

' pressor air.

profile across theturbine buckets, the centerbody is pro inner cone andangled to introduce air tangentially to the I inner surface of the coneas seenby the arrows in FIG. 2. I ThlS air tends to further break up theatomized'fuel introduced by an injecto r 25 whose spray angle conepattern is-adjusted to cornecloseto, but not impinge upon, thejuncture-of the inner and outer cones. Thus, the fuel sprayis containedwithin the inner cone without striking it but filling it. In thisvwaythe'formation of droplets is avoided-while atomization is enhanced.

Because the air entering by-louvers 24 tends to flow or Ispin outwardalong the liner wallscarrying entrained fuel, it is important to controlthis centrifuging action. To-this end, there is provided a second series=of-louvers 26 in the outer cone 23. Control is obtained by orientingthesemore'numerous louvers in an off radial direction as seen in FIG. 2.The air flow into louvers 26 is in i generally the same direction aslouvers24 as seen -by the arrows.

Additionally theair is also introduced tangentially as in louvers 24.However, because of the off radial orientation of louvers 26 located incone- 23, the'air flow also has a radial inward component of swirl tootfset the centrifuging action of the inner louvers and confine and mixthe flow into the cylindrical combustion zone in a'core off the walls ofthe liner. Thus, the walls are protected from the high combustionreaction temperature, I r

as well as the deposit and breakdown of fuel thereon. Since therintersectionvof the louvered flows creates a good recirculation and richfuel air mixture, it is-at this posed through the? dome member 15 andoutercone 23 between the louvers therein to ignite 'in this preferredarea.

An ig'nitoris disp essary, additional openings 36 canbe provided in thecenterbody.

Referring next to FIG. 3, the radial temperature profile across atypical turbine inlet annulus is indicated by p the line 37 which showsa cool tip and hot root port-ion.

In accordance with the invention, there is shown a radial temperatureprofile 38 across a turbine inlet annulus. The average temperature isshown by line 39. By providing cooling air guided by the centerbodytowards the root of the turbine buckets it is possible to, in effect,tilt the average temperature 39 to profile 38 providing a cool.-

' er root portion' which is the highly stressed portion and: a

tage is apparent.

The flatter outer cone 23 in conjunction with its off i radial louvers26 results in a strong flame stabilizer tending to hold or'anchor theflame in thefdomeend of the cylindrical part'of the combustor where'itis desired.I

Further cooling of the combustor liner is obtained by constructing thecombination conical-cylindrical liner in 1 a number of sections that arenested together as shown.-

; These sections are joined by spacing means such as ribbon strips 27which define air conduits 28 for the' passage of air axially along theinner surface of the liner; These;

strips may be bentas shown at the junction of the cone 7 andcylindricalfparts of the liner. In addition to cooling the liner, theentering air furthers the combustion process in the cylindrical part ofthe liner and, with the air entering holes 19 in the conical'portion,tends. to quench the flame andreduce the temperature of thegases-approaching turbine buckets 29. V V r r In order to direct thecombustion gas smoothly intorthe turbine 13 and 'obtain the desiredtemperature profile l combustion zone ahead of the turbine. nopenalty inperformanceeven when a large, percentage hotter tip portion which is thelow stressed portion. Thus, the turbine design is improved enabling agiven material to be used at higher turbine temperatures or, maintainingthe same temperature, to'minimize bucket weight and the associated diskloads. In either case an advan- 'If necessary or desirable, additionalopenings 4t) may be provided in cap 33 to cool the outer surface of thecap and mix with the hot core in the combustion zone. The closed forwardportion of the centerbody may also be provided with openings 41 for useof cooling air at additional points such as for turbine wheel cooling orfor oil sump seal pressurization; V V I The use of the centerbodypermits use of .the cooling air flowing through annulus 34 in'thethermodynamic cycle. In other words, the coolingair is returned to theThus, there is of the total engine airflow ispassed through the;centerbody for coolingpurposesQ Additionally, the'centerbody provides aconvenient means for introducing cool air to mix withthe hot centralcoreof'gas in liner 11 to prornote uniformity of'circumferential temperaturepattern at the turbinerinlet. It will be apparent thatsome of the airflowing along theouter surface of centerbody 30 mixes I with the hotcore combustion gas and therefore penetra tion of airthrough openings 19need not be as deep be acrossthe turbine buckets 29, a hollowcone-shaped cen- V terbody 30 is provided. As shown, the centerbody issupported centrally of'the combustion zone and extends axi-.

ally into inner liner 17. Support of the centerbody is ob tained byconnecting hollow turbine nozzles 31 with 'the liner concentric shell11. The hollow nozzles and 'hollow centerbody permit air in annularpassage '12 to pass also to the interior of the centerbody due to thepressure differential between the combustion zone and the com- In orderto obtain the desired temperature videdwith'an aperture means 32 in itscone. For guiding the cooling air, a dome cap 33cups the end of the coneof'centerbody 30 as shown and this provides an annular air metering duct34 completely around the cap.

7 Cap 33 is supported by any suitable means '35 from the centerbody andarranged so that the area of the annular duct 34 is equal to or smallerthan the area of aperture 32 in order to prevent aperture 32 being alimiting factor in the flow of metered cooling air. the cupping oroverlapping arrangement of cap 33 permits the air, duct 34 to cool thecap and to direct airforwardly along the centerbody outer surface tocool the outer surface and to direct a cooling toward the root portionsof turbine buckets 29. I If nee It can be seen that flow of air alongthe surface cause coolair is introduced from both s'idesthe centerbodyside as well as theliner side. Thus, for mixing lower.

purposes, thepenetration of the cool air may therefore be It is to benoted that perforations 19'of increasing area,

in liner 17 extend substantially from the end 20 of the liner back toapproximately the upstream end of dome cap 33' and that the remainder ofthe exit gas channel de- I fined by thecenterbody and liner isunperforated. This 7 is deliberately providedin order to allow thetemperature of the air at the walls to heat up sufiiciently to maintain.the proper bucket profile. .In other words, excessive cooling air on thewalls of the centerbody and the inner liner in the area 42, wouldrequire much hotter air in the I central portion in order to obtain thedesired average temperature. This would produce a temperature profile lacross the buckets as shown by dotted line 43 in FIG. 3.

Therefore it is desired to allow the exhaust gas in the area 42 to heatup the'air along the walls to obtain the desired temperature profile 38.V 7

It can be seen that the conical-cylindrical shapes of the elementsobtain 'the good air distribution and lightweight of my invention,obviously many modifications and variations of'thepresent invention arepossible in the light of 1 the above' teachings. It is therefore to beunderstood that within the scope of the appended claims, the inven tionmay be practiced otherwise than as specifically described. I

Iclaim:

1. A reverse flow combustion system adapted for use at the downstreamend of a gas turbine engine adjacent the turbine, said systemcomprising:

a pair of concentric shells defining an annular air passage around theturbine,

an outer combination conical-cylindrical closed casing secured to theouter shell,

an inner concentric combination conical-cylindrical and open-endedperforated liner secured to the inner shell,

said casing and liner being symmetrically spaced to continue saidannular air passage downstream,

a double conical dome member closing the open end of said linerincluding an inner cone and a continuing outer cone opening away fromsaid inner cone,

a series of substantially radial louvers around said inner cone,

a second series of louvers in said outer cone oriented off radial toprovide a component of flow radially inward of said liner,

a fuel injector through said dome member,

a hollow conical centerbody,

hollow turbine nozzles connecting said centerbody and inner shell tosupport said centerbody spaced centrally of said liner and to conductair to said centerbody,

aperture means in the cone of the centerbody,

and a dome cap supported on and spaced from said centerbody over saidaperture to provide an annular air metering duct to direct air forwardalong the centerbody surface.

'2. Apparatus as described in claim 1 wherein the inner linerperforations extend from said open end to substantially the upstream endof said dome cap.

3. Apparatus as decribed in claim 1 wherein ignition means is disposedthrough said dome member outer cone between the louvers of said secondseries.

4. Apparatus as described in claim 1 wherein the area of said apertureis at least equal to the area of said annular air metering duct and saiddome cap overlaps said centerbody to guide air flow along the outersurface thereof.

5. Apparatus as described in claim 1 wherein said innerconical-cylindrical liner consists of a plurality of nested sectionsspaced from one another by ribbon strips defining air conduitsconnecting said annular air passage with the interior of said liner.

6. A reverse flow combustion system adapted for use at the downstreamend of a gas turbine engine adjacent the turbine, said system beingsymmetrical about the engine center line and comprising,

a pair of spaced concentric generally conical members with their conesdirected aft including,

a first outer combination conical-cylindrical closed casing secured tothe outer shell,

a second inner open-ended combination conical-cylindrical perforatedliner connected to said inner shell,

said casing and liner being symmetrically spaced to continue saidannular air passage downstream,

a third inner hollow centerbody having an aperture in its cone,

hollow nozzles connected to the inner shell and to said centerbody tosupport said centerbody spaced from and extending into the conical partof said inner liner and to conduct air to said centerbody,

a double conical dome member closing the open end of said inner liner inthe cylindrical part thereof,

said dome member including an inner cone and a continuing outer coneopening away from said inner cone,

a series of substantially radial louvers around said in-' ner cone,

a second series of louvers in said outer cone oriented off radial toprovide components of flow tangentially and radially inward of saidliner for spiral fiow therein away from said liner walls, 7

a fuel injector through said dome member adapted to .spray fuel in apattern within said inner cone,

and a dome cap supported on and spaced from said centerbody over saidaperture to provide an annular air metering duct to direct air forwardalong the centerbody surface.

7. Apparatus as described in claim 6 wherein the inner linerperforations extend with increasing area from said open end tosubstantially the upstream end of said dome cap.

8. Apparatus as described in claim 6 wherein ignition means is disposedthrough said dome member outer cone between the louvers of said secondseries.

9. Apparatus as described in claim 6 wherein the area of said apertureis at least equal to the area of said annular air metering duct and saiddome cap overlaps said centerbody to guide air flow along the outersurface thereof.

10. Apparatus as described in claim 6 wherein said innerconical-cylindrical liner consists of a plurality of nested sectionsspaced from one another by ribbon strips defining air conduitsconnecting said annular air passage with the interior of said liner.

11. A' combustor including an outer combination conical-cylindricalcasing closed at one end,

an inner concentric combination conical-cylindrical and open-endedperforated liner, said casing and liner being spaced apart to provide anannular air passage therebetween. a double conical dome member closingan open end of said liner at said one end, said dome member inciuding aninner cone nad a continuing outer cone opening away from said innercone, :1 series of substantially radial louvers around said inner cone,

a second series of louvers in said outer cone oriented ofi radial,

and a fuel injector through said dome member,

whereby some air enters said liner through the radial louvers in saiddome member for atomizing fuel and some .air enters said liner from saidoff radial louvers in a tangential and radially inward direction tocreate swirl and keep fuel oil the liner wall.

12. A combustor including an outer combination conical-cylindricalcasing closed at one end,

an inner concentric combination conical-cylindrical and open-endedperforated liner,

said casing and liner being spaced apart and symmetrical to provide anannular air passage therebetween reducing in cross-sectional area in theconical part and substantially constant in the cylindrical part,

a double conical dome member closing an open end of said liner in thecylindrical part at said one end,

' said dome member including an inner cone and a continuing outer coneopening away from said inner cone,

a series of substantially radial louvers around said inner cone,

a second series of louvers in said outer cone oriented off radial toprovide components of flow tangen tially and radially inward of saidliner for spiral flow therein away fromsaid liner walls,

a fuel injector through said dome member centrally thereof to spray acone of fuel therein,

said inner and outer cones containing said fuel spray withoutimpingement thereon.

(References on following page)

1. A REVERSE FLOW COMBUSTION SYSTEM ADAPTED FOR USE AT THE DOWNSTREAMEND OF A GAS TURBINE ENGINE ADACENT THE TURBINE, SAID SYSTEM COMPRISING:A PAIR OF CONCENTRIC SHELLS DEFINING AN ANNULAR AIR PASSAGE AROUND THETURNINE, AND OUTER COMBINATION CONICAL-CYLINDRICAL CLOSED CASING SECUREDTO THE OUTER SHELL, AN INNER CONCENTRIC COMBINATION CONICAL-CYLINDRICALAND OPEN-ENDED PERFORATED LINER SECURED TO THE INNER SHELL, SAID CASINGSAID LINER BEING SYMMETRICALLY SPACED TO CONTINUE SAID ANNULAR AIRPASSAGE DOWNSTREAM, A DOUBLE CONICAL DOME MEMBER CLOSING THE OPEN END OFSAID LINER INCLUDING AN INNER CONE AND A CONTINUING OUTER OPENING AWAYFROM SAID INNER CONE, A SERIES OF SUBSTANTIALLY RADIAL LOUVERS AROUNDSAID INNER CONE, A SECOND SERIES OF LOUVERS IN SAID OUTER CONE ORIENTEDOFF RADIAL TO PROVIDE A COMPONENT OF FLOW RADIALLY INWARD OF SAID LINER,A FUEL INJECTOR THROUGH SAID DOME MEMBER,